Process for transparent photographic images

ABSTRACT

THIS INVENTION IS CONCERNED WITH A PROCESS OF PRODUCING PHOTOGRAPHIC IMAGES ON A TRANSPARENT SUBSTRATE BY PHOTOEXPOSURE OF A PHOTOGRAPHIC MEDIUM OF WHICH THE PHOTOSENSITIVE LAYER IS REMOVABLE FOLLOWED BY PROLONGED TREATMENT OF THE EXPOSED MEDIUM TO FORM A METAL IMAGE ADHERENTLY BONDED TO THE SUBSTRATE AND SUBSEQUENT REMOVAL OF THE PHOTOSENSITIVE LAYER TO OBTAIN THE METAL IMAGE ON THE SUBSTRATE, AS WELL AS THE PRODUCTS PRODUCED THEREBY.

United States Patent O flice Patented July 23, 1974 3,825,424 PROCESSFOR TRANSPARENT PHOTOGRAPHIC IMAGES Robert F. Gracia, Scituate, RichardA. Laughrey, Woburn, and Paul F. Tuohey, Quincy, Mass., assignors toItek Corporation, Lexington, Mass.

No Drawing. Application Oct. 1, 1969, Ser. No. 862,912, which is acontinuation-in-part of application Ser. No. 744,631, July 15, 1968,both now abandoned. Divided and this application Aug. 7, 1972, Ser. No.278,310

Int. Cl. G03c 5/24 US. CI. 9648 PD 21 Claims ABSTRACT OF THE DISCLOSUREThis invention is concerned with a process of producing photographicimages on a transparent substrate by photoexposure of a photographicmedium of which the photosensitive layer is removable followed byprolonged treatment of the exposed medium to form a metal imageadherently bonded to the substrate and subsequent removal of thephotosensitive layer to obtain the metal image on the substrate, as wellas the products produced thereby.

This case is a division of Ser. No. 862,912, filed Oct. 1, 1969, nowabandoned, which is a continuation-in-part of US. Ser. No. 744,631,filed July 15, 1968, now abandoned.

BACKGROUND OF THE INVENTION Field of the Invention This inventionrelates to developed photographic media and processes for theirproduction.

Description of the Prior Art In the process of producing photographicimages in transparent films, one of the difficulties encountered is thefog level which can develop in the photosensitive layer duringphotoprocessing. The development of fog in this layer necessitatesspecial care and control in not only photographic development of thelatent image but also in the selection and preparation of thephotosensitive layer on the film in the production hereof. Such stepsand precautions as are necessary to minimize fog, e.g. backgrounddensity, in transparent films are well known to those skilled in the artand should not require extensive documentation for the purpose of thisdisclosure. In transparent films in which the photosensitive material isa photoconductor, eig. titanium dioxide, care must be exercised to avoidthe milky background of such films during development, which, though notalways a significant problem, is met with some regularity in certainsituations.

SUMMARY OF THE INVENTION This invention relates to the process ofproducing photographic images on a transparent substrate byphotoexposing a photographic medium comprising a removablephotosensitive layer comprised of photosensitive material on atransparent support, contacting the photo-exposed medium with suitableimage-forming material preferably a physical developer, to form a metalimage in the exposed areas of the medium, prolonging the step ofcontacting with the image-forming materials until the formed metal imageis adherently bonded to the support, and finally removing thephotosensitive layer to obtain the metal image on the support. Themedium for use in the present process preferably includes a transparentsubstrate one face of which is superficially roughened and on which thephotosensitive layer is applied. A preferred process is one utilizing acopy medium capable of being rapidly processed and having a very thinlayer of a removable photosensitive layer on a superficially roughenedtransparent support. The rapid processing intended refers to contactingthe copy medium with room temperature chemicals, such as silver nitrateand a reducing agent therefor, to produce an image adherently bonded tothe support usually in less than about one minute.

DESCRIPTION OF PREFERRED EMBODIMENTS The production of a photographicmetal image which is adherent to the transparent substrate isaccomplished by physical development of the exposed medium. The extentof such development required to obtain an image adherently bonded to thesupport is determined by many factors such as the intensity of lightused during exposure, the concentration and type of reagents which makeup the physical developer system, the time of development, and similarsuch considerations which are well understood by those skilled inphotographic chemistry. A minimum of routine experimentation will permitthe selection of proper reagents and conditions to obtain a metal imageadherently bound to the substrate. For example, test strips of selectedmedia can be exposed, developed and then subjected to treatment forremoval of the photosensitive layer and the optimum conditions are thusdeterminable.

The photosensitive material of the present media can be any of thosewhich permit physical development of a metal image, i.e. physicallydevelopable photosensitive materials. This type of photosensitivematerial is known in the art and embraces those photosensitive materialswhich after photoexposure are developable by what is known as physicaldevelopment. Physical development is development using a solution ofreducible metal ions and a reducing agent therefor which willselectively deposit metal in the photo-activated areas. In theory, thefirst step of such development is the formation of a latent metal imagewhich is then intensified, or amplified, by the metal obtained byreduction of the aforesaid metal ions. The metal of the latent metalimage may be the same as the so-reduced metal or different, e.g., thelatent image can be silver and the so-reduced metal, copper or silver,as desired. In silver halide photography, the latent silver image formsin the silver halide emulsion and physical development is used to renderthe photo-image visible. Conveniently, the reducible metal ion forsilver halide film is already present in the photosensitive emulsion inthe form of the silver halide. However, an external source of reduciblemetal ion can be used in lieu thereof. Suitable photosensitive materialsinclude silver halides, such as silver chloride or bromide; azocompounds, e.g. as described in British Specification 1,064,726, amongothers; photoconductors, as described in British Specification1,043,250; ferric compounds; and methylene blue.

A physically-developed image can be:

(1) the image formed on photoexposure, eg. the latent silver image insilver halide emulsions or the reversible latent image on aphotoconductor;

(2) the irreversible image formed by contacting an exposedphotoconductor-bearing medium with a sensitiz ing metal ion, e.g. asolution of silver ion, which can lead to an invisible irreversibleimage or a visible metal image;

(3) the latent ferrous ion image formed by photoexposure of a ferricsalt-sensitized medium and then sensitized wtih silver ion solution toform a silver image; or

(4) a conductive image in close proximity but spaced from the supportand which may be produced photographically, by printing, by writing orby physically placing a metallic image adjacent to the support.

Of the photosensitive materials, especially preferred arephotoconductors, particularly as described hereinafter.

The preferred copy medium of this invention comprises a transparent baseor support with the photosensitive material present in a layer of bindermaterial. The copy medium especially preferred for use in this inventioncomprises a plastic base photographic plate capable of being stored inlight or darkness without deterioration of its photosensitive componentsand capable further of being physically developed comprising aphotoconductor which becomes reversibly activated upon exposure toactivating radiation and is capable of causing chemical reaction in theexposed areas, this photoconductor preferably being deposited upon asuperficially roughened support. The photoconductor is preferably of aparticulate nature, preferably incorporated in a photoconductivelyinsulating binder, and deposited as a very thin, removable layer uponthe support, especially on a superficially roughened support, in such away that the photoconductor is impregnated at least in part within theroughened surface of the support. This is readily accomplished forexample by depositing a photoconductor, such as TiO in a solvent-bindersolution of relatively low viscosity and then coating this compositiononto the roughened support. The coating composition may be allowed todry. Such a support which has a photoconductor-binder coating willpreferably have a very thin coating which is solvent permeable and willthereby allow rapid processing in the preferred developer systems.

The roughened support is a support which has been physically,chemically, or otherwise roughened in order that the metallic imageforming materials are adherently bonded to the support. Physicallyroughened supports which are suitable for this invention are ones havinggrained, porous, or matted surfaces. Chemically roughened supports areones which have been treated by suitable acids or bases, adhesiveprimers and the like to cause chemical bonding to take place between theimage forming materials and the surface of the support. Additionally,additives such as cadmium and/or zinc salts may be added to the imageforming materials in a manner such as described in French Patent ofAddition No. 77,556 in order to improve the adhesion of the metal imageto the support. The term roughened supports, therefore, is intended toinclude a physically smooth support which by chemical or other meansprovides an adhesive bond with the metal image deposited thereon.

With supports comprising a plastic, i.e. a transparent plastic, thephotosensitive layer is preferably coated on a subbed plastic sheet,such as sheets of a cellulose acetate, or a polyester, especiallypolyethylene terephthalate, containing a layer of material whichimproves the adhesion of the photosensitive layer to the plastic sheet.The intermediate layer is called a subbing layer, which concept is wellknown to the art. Usually, subbing layers comprise materials whichadhere to the plastic material and to the more hydrophilicphotosensitive layer. Generally, subbing layers are comprised ofgelatin, but may also comprise various latex polymers, such as variousvinylidene polymers, polyvinyl formals, polyvinyl butyral and similarsuch materials which are known in the art. The preferred subbing layersare those which imbibe the physical developer materials, for example,gelatins.

The thickness of the photosensitive layer or the imageforming layer, andthe insulating layer or subbing layer, where present, will depend uponthe nature of the photosensitive material, the nature of the binder,where present, the amount of activating radiation utilized, and otherlike factors. However, in order to obtain an imaging medium capable ofrapid processing it is preferred that these layers be relatively thin,preferably less than about 50 microns in thickness. However, thethickness of the photosensitive layer and the insulating or subbinglayer may vary within wide ranges. The coating thickness may be variedaccording to the effects desired. However, most preferable is asubstrate wherein the coating is less than 10 microns in thickness inorder to obtain the rapid processing which is most desired.

In general, the amount of binder to amount of photoconductor or otherphotosensitive material may vary over wide ranges. Preferably, fromabout 1 part by weight to about 6 parts by weight of photosensitivematerial per part by weight of binder will be used.

The photoconductor or photocatalyst preferred in this invention is ametal containing photoconductor. A preferred group of suchphotosensitive materials are the inorganic materials such as compoundsof a metal and a non-metallic element of Group VIA of the periodic tablesuch as oxides, such as zinc oxide, TiO zirconium dioxide, germaniumdioxide, indium trioxide; metal sulfides such as cadmium sulfide (CdS),zinc sulfide (ZnS) and tin disulfide (SnS metal selenides such ascadmium selenide (CdSe). Metal oxides are especially preferredphotoconductors of this group. TiO is a preferred metal oxide because ofits unexpectedly good photosensitive properties. TiO having an averageparticle size less than about 250 millimicrons and which has beentreated in an oxidizing atmosphere at a temperature exceeding about 200C. is especially preferred, and more especially TiO produced by hightemperature pyrolysis of titanium halide.

Organic photoconductors such as imidazolidinones and heteropolyacidsmentioned in US. Ser. No. 623,534, now Pat. No. 3,623,865, incorporatedherein by reference are also useful photosensitive materials in thisinvention.

Also useful in this invention as photoconductors are certain fluorescentmaterials. Such materials include, for example, compounds such as silveractivated zinc sulfide, and zinc activated zinc oxide.

While the exact mechanism by which the photoconductors of this inventionwork is not known, it is believed that exposure of photoconductors orphotocatalysts of this invention to activating means causes an electronor electrons to be transferred from the valence band of thephotoconductor or photocatalyst to the conductance band of the same orat least to some similar excited state whereby the electron is looselyheld, thereby changing the photoconductor from an inactive form to anactive form. If the active form of the photoconductor or photocatalystis in the presence of an electron accepting compound a transfer ofelectrons will take place between the photoconductor and the electronaccepting compound, thereby reducing the electron accepting compound.Therefore, a simple test which may be used to determine whether or notmaterials have a photoconductor or photocatalytic effect is to mix thematerial in question with an aqueous solution of silver nitrate. Little,if any, reaction should take place in the absence of light. The mixtureis then subjected to light. At the same time a control sample of anaqueous solution of silver nitrate alone is subjected to light, such asultraviolet light. If the mixture darkens faster than the silver nitratealone, that material is a photoconductor or photocatalyst.

It is evident that the gap between the valence and the conducting bandof a compound determines the energy needed to make electron transitions.The more energy needed, the higher the frequency to which thephotoconductor will respond. It is known to the art that it is possibleto reduce the band-gap for these compounds by adding a foreign compoundas an activator which either by virtue of its atomic dimensions or bypossessing a particular electronic forbidden zone structure or throughthe presence of traps or donor levels in the intermediate zone betweenthe valence and the conduction band stresses the electronicconfiguration of the photoconductive compound, thereby reducing itsband-gap and thus increasing its ability to release electrons to itsconduction band. Phosphors almost necessarily imply the presence of suchactivating substances. The effect of such impurities may be such as toconfer photoconductivity upon a compound which intrinsically isnon-photoconductive. On the other hand, excessive impurity content caninterfere with a compound acting as a photoconductor, as abovedescribed.

The photoconductors may be sensitized to visible and other wavelengthsof light by foreign ion doping, addition of fluorescent material, and/orby means of sensi tizing dyes. Bleachable dyes useful for sensitizingthe photoconductors include, for example, the cyanine dyes, thedicarbocyanine dyes, the carbocyanine dyes, and the hemicyanine dyes.Additional dyes which are useful for sensitizing the photoconductor arethe cyanine dyes described on pages 371-429 in The Theory ofPhotographic Process by C. E. Kenneth Mees published by McMillan Companyin 1952. Other useful dyes include those known to the art astriphenylmethane dyes such as crystal violet and basic Fuchsin,diphenylmethane dyes such as Auroamine O, and Xanthene dyes such asRhodamine B.

The photosensitive material is used in a binder to form thephotosensitive layer on the support, the sole requirement being that thelayer be removable after photoprocessing. For removal, various methodscan be used including dissolution or dispersion of the photosensitivelayer using suitable liquid systems, such as solvents for the binderemployed. Alternatively, removal of this layer with reactive solventssuch as alkali or acid can be used, e.g. aqueous sodium carbonate,dilute sodium hydroxide, dilute phosphoric acid, phosphate salts andsimilar reagents. Mechanical removal of the photosensitive layer can beemployed, e.g. using abrasive materials. Combinations of these methodscan be used, e.g. rubbing the photosensitive layer from the support inthe presence of a binder solvent or dispersing agent such as water.Other methods, e.g. gamma radiation ofcertain binders, can be used torender the layer frangible and it can then be removed mechanically.

Thus, the binders for use in the present media can comprise any of awide variety of materials known in the photographic art. In general,these binders are translucent or transparent so as not to interfere withtransmission of light therethrough. They are desirably also solventpermeable in order to allow rapid physical development to take place.Preferred binder materials are organic materials such as natural orsynthetic polymers. Examples of suitable synthetic polymers arebutadiene-styrene copolymer, poly(alkyl acrylates) such as poly(-methylmethacrylate), polyamides such as polyacrylamide, polyvinyl acetate,polyvinyl alcohol and polyvinylpyrrolidone. Natural polymers such asgelatin are also useful. Most preferred are those binders which aresolvent soluble enough to be readily washed off after development of theimage has taken place. Preferably, for convenience the binder should beremovable with aqueous systems. When not so removable, then suitablesolvents which will dissolve or disperse the binder should be used.Little difiiculty is encountered in selecting an appropriate solventsystem since a simple solubility test can be used for the said purposeby merely immersing test media consisting of the support coated with theselected binder in various solvent systems. Solubility data for mostbinders are usually provided in standard texts or otherwise available.For example, methyl ethyl ketone, methyl isobutyl ketone, acetone,tetrahydrofuran, dioxane, and similar polymer solvents will be useful.

To obtain metal images according to this invention, the binder shouldnot be removable by the photoprocessing conditions, i.e. thephotosensitive layer should remain substantially intact during solutionprocessing. However, if desired, binders which would dissolve in theprocessing solution during processing can be employed if viscousprocessing materials are employed, thus avoiding any substantialdissolution of the binder.

When employed as the photosensitive material, the photoconductor shouldbe conditioned for exposure by storage in the dark from one totwenty-four hours prior to use, heating or other conditioning meansknown to the art. After conditioning the photoconductor is not exposedto activating radiation prior to its exposure to activating radiationfor recording an image pattern.

The period of exposure to form the latent image will depend upon theintensity of the light source, particular photosensitive material, thetype and amount of catalyst, if any, and like factors known to the art.In general, however, the exposure may vary from about 0.001 seconds toseveral minutes.

When the photosensitive material comprises a photoconductor, azocompounds, or ferric compounds, the physical developers according tothis invention are intended to include those image forming systems suchas described in US. Pat. 3,152,903, in British Patent Specification No.1,043,250 and British Pat. 1,064,725. These image-forming materialsinclude preferably an oxidizing agent and a reducing agent. Suchimage-forming materials are also often referred to in the art aselectroless plating baths. Electrolytic development such as taught inUS. Pat. 3,152,969 can also be used. The oxidizing agent is generallythe image-forming component of the imageforming material. Either organicor inorganic oxidizing agents may be employed as the oxidizing componentof the image-forming material. The oxidizing and reducing agent may becombined in a single processing bath, may also be in separate bath, orone or both of these components may be incorporated in the imagingmedium prior to exposure. Preferred oxidizing agents comprise thereducible metal ions having at least the oxidizing power of cupric ionand include such metal ions as Ag Hg, +1 +s p +2 n+4 +2 +2 b+2 cut-1 andCu.

When the photosensitive material comprises a silver halide, the physicaldevelopers can comprise a solution of an amplifying metal ion, e.g.silver, copper, tin and like ions with a reducing agent therefor, or thephysical developer can comprise a silver reducing agent and a solventfor the silver halide. The silver halide solvents are well known in thephotographic art and include any substance which will dissolve theunexposed silver halide of the photosensitive layer to form a solutionthereof which functions as an amplifying agent for the latent imageformed by the photoexposed silver halide. Commonly employed as silverhalide solvents are soluble thiosulfate and thiocyanate salts, but anysalt capable of dissolving silver halide, usually by complex ionformation, can be used for the same purpose as long as the complex ionformed is not of a high order of stability, i.e. not appreciablydissociated.

The reducing agent component of the said image-forming materials areinorganic compounds such as the oxalates, formates, andethylenediaminetetraacetate complexes of metals having variable valence;and organic compounds such as dihydroxybenzenes, aminophenols, and aminoanilines. Also, polyvinylpyrrolidone, hydrazine, and ascorbic acid maybe used as reducing agents in this invention. Suitable specific reducingcompounds include hydroquinone or derivatives thereof, 0- andp-aminophenol, p-methylaminophenol sulfate, p-hydroxyphenyl glycine,oand pphenylenediamine, 1-phenyl-3-pyrazolidone, alkali and alkalineearth metal oxalates and formates.

Liquid physical developer systems are preferred for use as image-formingmaterials because of the excellent results obtained therewith. Anysuitable solvent may be utilized. However, aqueous processing baths arepreferred. While the pH of the developer is not critical, it has beenfound that the best results are obtained with an acid developer, andespecially one having a pH of between about 2 and 5, and especially withorganic acids such as citric, gluconic, maleic, and oxalic which aremetal complexing agents. A pH of about 2 to 3 is especially preferred.

Additionally, the image-forming materials or physical developers maycontain organic acids or alkali metal salts thereof, which can reactwith metal ions to form complex metal anions. Further, the developersmay contain other complexing agents and the like to improve imageformation and other properties found to be desirable in this art.

Additional developer systems useful in this invention are thosedisclosed in the following US. Patent Applications filed on July 11,1968: Ser. No. 743,981, now Pat. No. 3,674,489, Ser. No. 743,982, nowabandoned, and Ser. No. 743,983, now Pat. No. 3,645,736, each of whichare incorporated herein by reference.

The physical developers of this invention should be applied for a lengthof time sufficient to obtain an image adherently bound to the support.This time period will vary according to the thickness of thephotoconductor layer or thickness of the insulating layer or otherseparation layers, the length of exposure, nature of the binder orinsulator material, ratio of photosensitive material to binder, and likefactors known to the art.

The following examples are given to further illustrate the invention:

EXAMPLE 1 A layer of titanium dioxide in polyvinyl alcohol is coated ona gelatin-nitrocellulose subbed cellulose triacetate sheet, thegel-subbing serving as the hydrophilic subbing and the polyvinyl alcohollayer as the easilyremoved layer.

The coated sheets is exposed through a negative to a quartz-iodide lampat 3 feet for 0.5 seconds and then processed by immersion for seconds in3 M AgNO (aqueous) followed by seconds in a saturated solution of Metolcontaining 80 g./l. of citric acid monohydrate.

Gentle rubbing under a stream of running water removed the polyvinylalcohol layer and a silver image is left in the gel-subbing layer. Theresult is a silver image on a transparent background.

Similar results are obtained when the photosensitive material is aferric compound, azo compound or silver halide in a binder to form aremovable layer.

When the triacetate sheet is replaced by a polyethylene terephthalatesheet, almost identical results are obtained.

This same procedure is used with a surface roughened polyethyleneterephthalate sheet coated on the roughened side with the photosensitivelayer without a subbing layer to obtain the silver image in theroughened surface of the sheet after removal of the developedphotosensitive layer. The surface of the sheet is roughened by rubbingwith an abrasive material.

EXAMPLE 2 A cellulose triacetate sheet with a roughened surface iscoated with a layer of photosensitive silver bromide in polyvinylalcohol exposed through a negative to actinic light and developed in asolution of hydroquinone containing 60 g./l. of sodium thiosulfate.

The polyvinyl alcohol layer is removed as in the preceding example toobtain a silver image in the roughened surface of the sheet.

EXAMPLE 3 A titanium dioxide coating, in which the pigmentbinder ratioof titanium dioxide to polyvinyl alcohol is 6-1 and the total solids is8%, is coated on a gelatinnitro cellulose subbed film. The coating isapplied with a No. 4 Meyer rod, or the coating can be applied via a diptechnique. The coated sheet is then exposed in a conventional way anddeveloped in the following bath for 90 seconds:

Solution I: G. Fe(SO (NH -6H O 78.4 Fe(NO -9H O 33.2 Tartaric acid 80.0Distilled H O to 1 1.

Solution II:

Armac 12D 1.0 Lissapol N 1.0 Distilled H O to 1 1.

Solution III:

3 N AgNO The bath is made up in the following ratio:

Ml. Solution I 125 Solution II 25 Solution III 6 The coating is thenremoved by gentle rubbing of the surface. A diffused image remains inthe subbing layer.

EXAMPLE 4 A titanium dioxide coating as described in Example 3 is coatedon a subbed film and the subsequently exposed film is developed in thefollowing solution:

Solution I: G. Metol 1 30 Citric acid 1 Solution II:

3 N AgNO T0 1 liter.

150 cc. of Solution I are mixed with 5 cc. of Solution -II just prior todevelopment. The exposed film is developed for seconds. The top coatingis removed and a diffused silver image remains on the substrate.

EXAMPLE 5 A subbed polyester film base is coated with a finely dividedtitanium dioxide pigment dispersed in a polyvinyl alcohol binder. Thepigment to hinder ratio on a weight basis is 3:1 and the total solids ofthe emulsion is 15% by weight. The film base is coated on a rollercoater yielding approximately 0.40 grams of titanium dioxide per squaremeter. The coated film is then dried and exposed with a quartz iodinelamp at a distance of 30 inches from the target through a vacuumprinting frame for 2 seconds. After 10 seconds from the exposure thesample is processed with a stabilized physical developer for 3 minutes.The physical developer is of the following formulation:

Solution I: G. Fe(NH4)2(SO4)26H2O Fe(NO -9H O 25.2 Tartaric acid 80.0 HO to 1 liter.

Solution II:

Armac 12D (ionic surfactant) 1.0 Synthrapol N (nonionic surfactant) 1.0

H 0 to 1 liter.

Solution III:

AgNO 51.0 H O to ml.

The bath is made up in the following ratio:

Ml. Solution I 250 Solution II 50 Solution III 6 The developed film isthen placed in a tray of water at room temperature and wiped with a softcotton pad to remove the coating. The resulting clear transparency has amaximum optical density of about 3.0. The image adhesion is tested byplacing a strip of Scotch Brand tape over it and removing the tape witha quick pull. No silver is removed from the image area by this test. Onesample of the processed film is contacted with an oleophilic lacquerwhich makes the film suitable for use as a lithogrraphic master. Asecond sample in the form of a movie film strip with a variable areasound track adjacent to the photographic images is amplified with anickel electroless plating solution in a manner such as described in thepatent application filed on even date entitled Photographically PreparedMagnetic Information Storage Element by Laura Case. The photographicimages on the movie film strip are of continuous tone and the variablearea soundtrack can be read out with an ordinary magnetic reading head.

EXAMPLE 6 A layer of silver chloride in polyvinyl alcohol is coated on asubbed triacetate, the coating acting, as an easily removed layer. Thesilver halide emulsion is made up in the following manner:

SILVER HALIDE EMULSION Component I:

Component II is poured into Component I rapidly while stirring. A milkywhite emulsion of very fine particle size results. The emulsion is thensonified for four minutes on a Bronson sonifier, coated on a film basewith a No. 4 Meyer rod, after which the coating is dried at 70 F. forfive minutes. It is then exposed in a conventional manner and processedin any of the physical developers described in the other examples. Thetop is removed and a diffused image results in the subbed layer. Thus,an imaged film with excellent transparency is produced.

The same results are obtained using a polyester film in lieu ofcellulose acetate film.

In the foregoing examples, the final products consist of the developedmetal image on the transparent substrate. These products are especiallysuitable for photocopying and projection, e.g. projection slides.Further treatment of these products by conventional methods convertsthem into printing masters, e.g. increasing the oleophilic nature of themetal image on a comparatively hydrophilic substrate renders the imagesink receptive. Thus, the metal images can be treated with mercaptanand/or lacquered by art-recognized procedures commonly employed inpreparing printing plates and then inked and used as a printing master.

The present invention can also be employed in the formation of printedelectrical circuits and the metal circuit is obtained on the transparentsupport. The metal circuit can be further amplified with a desiredmetal, e.g. copper, using standard procedures including electrolyticplating and electroless plating by art-recognized procedures. Theinitially developed metal circuit is comprised of a continuous,electrically-conductive metal image which is formed of large, contiguousparticles of the metal which gives the appearance of a continuous layer.This form of image is preferred for use in printing masters and inprinted electrical circuits.

In the foregoing examples, little if any special care has to be observedregarding fog development in the photosensitive layer since thephotosensitive layer is subsequently removed. After removal of thephotosensitive layer, the final products retain the originaltransparency of the substrate.

The term pellucid as used herein is intended to mean transparent ortranslucent. The above description while using the term transparent isintended to include a pellucid copy medium.

What is claimed is:

1. A process of producing a photographic metal image on a roughenedpellucid support therefor which comprises the steps of:

(a) exposing a copy medium comprising a thin removable layer comprisedof photosensitive material in a binder therefor on a pellucid support toform a physically developable image in said medium;

(b) physically developing by contacting the exposed medium withimage-forming material comprising a solution of metal ions to form ametal image in the exposed areas of the medium;

(c) prolonging the step of contacting with the imageforming materialsuntil the formed metal image is adherently bonded directly to thesupport; and

(d) removing the photosensitive layer and leaving the metal image on thesupport.

2. Process as in Claim 1 wherein the removable layer comprises asolvent-removable binder for the photosensitive material.

3. Process as in Claim 1 wherein the support is a subbed plastic sheet.

4. Process as in Claim 3 wherein the plastic is a cellulose acetate.

5. Process as in Claim 3 wherein the plastic is a polyester.

6. Process as in Claim 3 wherein the plastic is polyethyleneterephthalate.

7. Process as in Claim 3 wherein the subbed sheet is a gelatin-subbedsheet.

8. Process as in Claim 1 wherein the photosensitive material comprises aphotoconductor.

9. Process as in Claim 1 wherein the photosensitive material comprises aphotosensitive silver halide.

10. A process of producing a photographic metal image on a pellucidsupport therefor which comprises the steps of:

(a) exposing a copy medium comprising a thin removable layer comprisedof titanium dioxide in a binder therefor on a pellucid support to form aphysically developable medium in said medium;

(b) contacting the photo-exposed medium with a physical developercomprising a solution of reducible metal ions to form a metal image inthe exposed areas of the medium;

(c) prolonging the step of contacting with the imageforming materialsuntil the formed metal image is adherently bonded directly to thesupport; and

(d) removing the titanium dioxide layer and leaving the metal image onthe support.

11. Process as in Claim 10 wherein the removable layer comprises asolvent-removable binder for the photosensitive material.

12. Process as in Claim 10 wherein the support is a subbed plasticsheet.

13. Process as in Claim 10 wherein the plastic is a cellulose acetate.

14. Process as in Claim 10 wherein the plastic is a polyester.

15. Process as in Claim 10 wherein the plastic is polyethyleneterephthalate.

16. Process as in Claim 10 wherein the subbed sheet is a gelatin-subbedsheet.

17. Process as in Claim 10 wherein the reducible metal References Citedf Silver Cl 10 h th h 1 d UNITED STATES PATENTS rocess as in am w erem ep yslca eveloper comprises a reducing agent for the metal ions. a igg''ai' 19. Process as in Claim 18 wherein the metal is silver 5 340942911/1968 Egnan et a1 9648 P0 or copper.

20. Process as in Claim 10 including the further step 3152903 10/1964Shephard u 96 64 of amplifying the metal image after removal of the ti-RONALD H. SMITH, Primary Examiner tamum dloxlde layer' 10 E. C. KIMLIN,Assistant Examiner 21. Process as in Claim 20 wherein the amplifyingstep is accomplished with a silver, copper or tin ion solution includinga reducing agent for the selected metal ions. 96-1 R, 1.5, 1.8, 87 R

